Implement missing libxpc functions

[LubosD]

Darling takes libxpc from NextBSD, but a lot of APIs are missing:

• [ ] xpc_copy_entitlements_for_pid
• [ ] xpc_strerror (#ifdefed out?!)
• [x] xpc_dictionary_set_mach_recv
• [x] xpc_dictionary_set_mach_send
• [x] xpc_dictionary_copy_mach_send
• [ ] xpc_dictionary_get_audit_token
• [ ] xpc_copy_entitlement_for_token
• [ ] xpc_domain_server
• [x] xpc_pipe_try_receive
• [x] xpc_pipe_routine_reply

[bugaevc]

• [x] xpc_data_get_bytes
• [x] xpc_equal
• [x] xpc_fd_create
• [x] xpc_array_dup_fd
• [ ] xpc_array_set_fd
• [ ] xpc_array_get_connection
• [x] xpc_array_set_connection
• [x] xpc_connection_cancel
• [x] xpc_connection_get_name
• [x] xpc_connection_set_finalizer_f
• [x] xpc_endpoint_create
• [ ] xpc_transaction_begin
• [ ] xpc_transaction_end
• [ ] mpack2xpc_extension

[LubosD]

We could pull some fixes done in here: https://github.com/PureDarwin/launchd-and-libxpc/tree/master/src/libxpc

[npyl]

@LubosD @bugaevc There is a pull request from the same person who implemented xpc that applies some fixes. Hope this helps.

[npyl]

Like https://github.com/PureDarwin/launchd-and-libxpc/pull/3/commits/b8d5d0494e623c3da2cae4bfc210be523554131f

[LubosD]

@npyl Done. Copied all changes done in libxpc.